1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a facsimile, and a printer; and a lubricant applicator that is configured to be used for the image forming apparatus.
2. Description of the Related Art
Conventionally, a lubricant applicator that applies a lubricant onto a surface of an image carrier is known to aim improvement in a cleaning performance, improvement in a product life, and improvement in a transfer performance of a photosensitive element and an intermediate transfer belt each of which is an image carrier (for example, Japanese Patent Application Laid-open No. 2006-208437). As a typical configuration of a lubricant applicator, an application roller as a lubricant application unit, such as a brush roller or a sponge roller, is rotatably provided such that its outer circumferential surface is to be in uniform contact with an image carrier surface. A solid lubricant that is solidified from, for example, zinc stearate, is pressed onto the application roller by a lubricant biasing unit, for example, a compression spring, via a lubricant holding member. Accordingly, the solid lubricant comes in contact with the application roller while ensuring a certain pressure. With rotating, the application roller scrapes the solid lubricant and applies it onto the image carrier surface.
According to the lubricant applicator, because the solid lubricant is scraped as it is used, the height of the solid lubricant in the pressing direction becomes lower, meanwhile the spring length of the compression spring is extending. As the spring length extends, the spring pressure decreases and then the pressing force decreases, consequently, the quantity of a lubricant shaved by the application roller turns less, and the quantity of application onto the image carrier is decreased. For this reason, the quantity of application of the lubricant onto the image carrier varies from the beginning over time, so that there is a possibility that the above effects, such as improvement in a cleaning performance, improvement in a product life, and improvement in a transfer performance, may not be obtained over time.
To suppress change in the quantity of application of the lubricant onto the image carrier from the beginning over time, it is desirable to control reduction in the spring pressure over time by setting the spring constant of the compression spring to a low value. However, many of compression springs of which spring constant is set to a low value have a long free length compared with a length that is required in an actual use, and the diameter of wire of the spring is thin, consequently, there is a disadvantage that buckling tends to occur in the spring due to a pressure applied to the spring when the spring is mounted.
As a method of mounting a lubricant applicator, there are methods as described below. For example, as shown in FIG. 9, there is a method by which a solid lubricant 5 held by a lubricant holding member 5a to which a compression spring 7 is fixed is mounted to a housing 13 shaped in a box that has an opening on a side facing to an image carrier, and then an application roller 4 is mounted. In the apparatus, as the application roller 4 is mounted, the compression spring 7 becomes to press the solid lubricant 5 with a certain pressure. However, buckling tends to occur in the compression spring 7 at a contact point with the housing 13 shaped in box to which the compression spring 7 is not fixed, due to a pressure applied to the compression spring 7 when the compression spring 7 is mounted to the housing 13 (see FIG. 10). Furthermore, even when buckling occurs in the compression spring 7, it cannot be visually confirmed to mount the compression spring 7 again.
Moreover, as another example, as shown in FIG. 11, there is a method by which the application roller 4 is mounted to a frame 15a having an opening 16 also on an opposite side additionally to the side facing to the image carrier, and then after the solid lubricant 5 is mounted from the opening 16 on the opposite side, a cover 15b is mounted on the opening 16 on the opposite side. Notches 15c are provided on part of the cover 15b, and then a small lid 15d to which the compression spring 7 is fixed is fitted into each of the notches 15c, the compression spring 7 becomes to press the solid lubricant 5 with a certain pressure. However, also according to the apparatus, buckling easily occurs in the compression spring 7 at a contact point with the solid lubricant 5 to which the compression spring 7 is not fixed, due to being pressed when being mounted to the housing (including the frame 15a, the cover 15b, and the lids 15d). Furthermore, even when buckling occurs in the compression spring 7, it cannot be visually confirmed to mount the compression spring 7 again.
Moreover, Japanese Patent Application Laid-open No. 2006-201565 describes a method by which a compression spring is fixed to a lubricant holding member for a solid lubricant; a lid is provided on the other end of the compression spring, which is fixed to the lid with an adhesive seal, etc.; and the lid is fixed to an upper cover of a housing; so that the compression spring becomes to press the solid lubricant with a certain pressure.
According to the apparatus described in the Patent Document No. 2006-201565, because the both ends of the compression spring are fixed, buckling is more difficult to occur in the compression spring than in a compression spring that is not fixed. However, because the compression spring is pressed at once from a free length to a spring length in which the compression spring presses the solid lubricant with a certain pressure, there was a case in which a mounting defect was produced such that the fixing by the abovementioned adhesive seal, etc. comes off with an impetus, and buckling occurred in the compression spring. In this way, even according to the Patent Document No. 2006-201565, a countermeasure against buckling of a compression spring due to a pressure applied to the compression spring when compression spring is mounted to a housing is not sufficient.